Engineering Commons^™

Investigation Of Gallium Nitride Transistor Reliability Through Accelerated Life Testing And Modeling, Bradley D. Christiansen

Theses and Dissertations

Gallium nitride high electron mobility transistors are attractive to the DoD for their ability to operate at high frequencies, voltages, temperatures, and power. Yet, there are concerns about the reliability of these devices. Various degradation mechanisms and their causes are proposed in the literature. A variety of reliability tests were conducted to understand these mechanisms and causes. A multi-stressor experiment revealed different failure mechanisms than are in the literature. In particular, the devices tested at high voltage in the OFF state did not degrade significantly as suggested by others' reports. The validity of temperature-accelerated life testing when applied to GaN …

Development Of A Structured Concrete Thermocline Thermal Energy Storage System, Bradley M. Brown

Graduate Theses and Dissertations

The past couple of decades have shown a concern when considering the way the world obtains its power. The focus has been switching from fossil fuels that have been used for hundreds of years to renewable energy sources, such as the sun. Solar energy is readily and infinitely available for harnessing. One problem with solar energy, though, is its inability to be used during the night time and during cloud covered weather. A solution to this problem is the use of energy storage mechanisms. For solar plants that use solar thermal energy (concentrating solar power plants), thermal energy storage (TES) …

The Effects Of Solvent Mixture On The Thermal And Mechanical Properties Of Solvent Cast Poly-Lactic Acid (Pla) Film, Jeremy Hughes

All Theses

CH 1 ABSTRACT
The objective of this study was to investigate the effects of various solvents on the crystallinity and thermal expansion stability of PLA film. Three different PLA films were produced by the solvent casting technique; PLA in chloroform (PLA-C), PLA in methylene chloride (PLA-M), and PLA in methylene chloride: acetonitrile = 50: 50 (PLA-MA). The PLA-MA had higher % crystallinity, 46.15, than the PLA-C, 24.03, and the PLA-M, 14.25. With this increase in crystallinity, the PLA-MA had improved thermal expansion stability as shown by very low accumulated dimensional changes at 20-100 ¡C. Wide angle x-ray diffraction identified multiple …

Electronic And Magnetic Excitations In Graphene And Magnetic Nano-Ribbons, Maher Zakaria Ahmed Selim

Electronic Thesis and Dissertation Repository

The discovery of graphene - a 2D material with superior physical properties - in 2004 was important for the intensive global research to find alternatives to three-dimensional (3D) semiconductor materials in industry. At the same time there have been exciting advances for 2D magnetic materials on the nanometer scale. The superior properties of graphene are mainly attributed to its crystal structure and its relatively short-range interactions. These properties show that natural and artificial 2D materials are promising for new applications.

In this thesis we have carried out a comprehensive investigation of the effects of the 2D lattice structures, the roles …

Vibration-Based Health Monitoring Of Multiple-Stage Gear Train And Differential Planetary Transmission Involving Teeth Damage And Backlash Nonlinearity, Andrew Patrick Sommer

Master's Theses

The objective of this thesis is to develop vibration-based fault detection strategies for on-line condition monitoring of gear transmission systems. The study divides the thesis into three sections. First of all, the local stresses created by a root fatigue crack on a pinion spur gear are analyzed using a quasi-static finite element model and non-linear contact mechanics simulation. Backlash between gear teeth which is essential to provide better lubrication on tooth surfaces and to eliminate interference is included as a defect and a necessary part of transmission design. The second section is dedicated to fixed axis power trains. Torsional vibration …

Modeling And Development Of A Mems Device For Pyroelectric Energy Scavenging, Salwa Mostafa

Doctoral Dissertations

As the world faces an energy crisis with depleting fossil fuel reserves, alternate energy sources are being researched ever more seriously. In addition to renewable energy sources, energy recycling and energy scavenging technologies are also gaining importance. Technologies are being developed to scavenge energy from ambient sources such as vibration, radio frequency and low grade waste heat, etc. Waste heat is the most common form of wasted energy and is the greatest potential source of energy scavenging.

Pyroelectricity is the property of some materials to change the surface charge distribution with the change in temperature. These materials produce current as …

Cushop: A Simulated Shopping Environment Fostering Consumer-Centric Packaging Design & Testing, Charles Tonkin

All Dissertations

Consumer product packaging provides product damage protection, extends product shelf life, and communicates product usage instructions to the consumer. Its collective contribution to the waste stream is notorious, but its role in product salability is much less understood. Consumers now make the majority of product purchase decisions while present at the shelf, and since they do it very quickly (within 5-8 seconds), and do not appear to adhere to strong brand loyalty as was once more common, packaging (and more specifically, its aesthetics and contrast with its competitors) plays a dominant role in the decision-making process. It is difficult, however, …

Effect Of Different Oxygen Barrier Pouches On The Quality Of Retorted Carrots, Sarah Khor

All Theses

Thermally processed (TP) baby carrots were packaged in pouches with varying oxygen transmission rate (OTR) pouches. The pouches were four layer laminate (PET-Nylon-Barrier-CPP) with barrier layer being foil, aluminum oxide (AlOx), ethylene vinyl alcohol (EVOH), and nylon. Retort pouches were placed in boxes that were stored in an environmental chamber (43 °C, 50%RH). The objective of the study was to determine an alternative barrier retort pouch that is microwavable and still had similar barrier functions to foil for baby carrots and determine how the alternative compare with regard to shelf life. Instrumental analysis of color (L*, a*, b*) and texture …

The Effect Of Barrier Properties Of Non-Foil Retort Films On Shelf Life Of Oxygen Sensitive Foods, Mahalaxmi Dharman

All Theses

A simulated food product sensitive to oxygen, which was a mixture of tomato paste, water, and corn oil (2:2:1), was filled into five different barrier coated pouches, a foil barrier and a low barrier pouch. These pouches were thermally processed at 250¡F for 30 minutes and stored in darkness under accelerated conditions (45±2¡C and 50±2%RH) for up to 180 days.
The simulant was analyzed for lipid oxidation by TBARS and lycopene degradation by colorimetry (L*,a*,b* values and Hue angle). The oxygen permeability (OP) in all the pouches increased by 5 to 500 fold after retort. TBARS values in all pouches …

Friction Bit Joining Of 5754 Aluminum To Dp980 Ultra-High Strength Steel: A Feasibility Study, Britney Weickum

Theses and Dissertations

In this study, the dissimilar metals 5754 aluminum and DP980 ultra-high strength steel were joined using the friction bit joining (FBJ) process. The friction bits were made using one of three steels: 4140, 4340, or H13. Experiments were performed in lap shear, T-peel, and cross tension configurations, with the 0.070" thick 5754 aluminum alloy as the top layer through which the friction bit cut, and the 0.065" thick DP980 as the bottom layer to which the friction bit welded. All experiments were performed using a computer controlled welding machine that was purpose-built and provided by MegaStir Technologies. Through a series …

The Effects Of Damage Arrestment Devices In Composite Plate Sandwiches With Fastener Holes, Mark Anderson, Nancy Hung Choy, Lacey Jones, Rita Kourskaya

Aerospace Engineering

Composite materials such as a carbon fiber are used in a variety of new technologies including aircraft, spacecraft, and motor vehicles. Carbon fiber has a high strength to weight ratio, a key advantage over other material options. This report discusses the use of composite damage arrestment devices (DADs) in composite sandwich panels with a foam core. There are three different curing cycles tested for the DADs: pressure only, vacuum only, and vacuum with 1000 lbs of pressure. Using a Tetrahedron Heat Press to cure the composite specimen and an Instron Machine to perform tensile testing, data was collected for each …

Plasma Processing Of Poly(Ethylene Terephthalate) (Pet) In An Oxygen Decoupled Plasma Source, Russell L. Rhoton

Master's Theses and Doctoral Dissertations

No abstract provided.

Development And Analysis Of Onboard Translunar Injection Targeting Algorithms, Phillippe Lyles Winters Reed

Masters Theses

Several targeting algorithms are developed and analyzed for possible future use onboard a spacecraft. Each targeter is designed to determine the appropriate propulsive burn for translunar injection to obtain desired orbital parameters upon arrival at the moon. Primary design objectives are to minimize the computational requirements for each algorithm but also to ensure reasonable accuracy, so that the algorithm’s errors do not force the craft to conduct large mid-course corrections. Several levels of accuracy for dynamical models are explored, the convergence range and speed of each algorithm are compared, and the possible benefits of the Broyden and trust-region targeters are …

Tool Life Of Various Tool Materials When Friction Spot Welding Dp980 Steel, Christopher Shane Ridges

Theses and Dissertations

In this study, friction spot welding was used to join DP980 steel sheet. Four different ultra-hard tool materials were used with the objective of determining which tool material produced the highest number of acceptable-strength welds. Three of the tools were composed of various mixtures of polycrystalline cubic Boron Nitride (PCBN), Tungsten, and Rhenium. These materials are referred to herein as Q60, Q70, and Q80, the "Qxx" designation denoting the percentage of the volume of the tool material composed of PCBN. The fourth tool tested was composed entirely of PCBN. The Q70 tool produced approximately 1100 welds of acceptable strength before …

Material Reduction In Corrugated Containers For The Fresh Produce Industry, Justin Patterson

Industrial Technology and Packaging

In the fresh produce industry, corrugated containers must be made to provide adequate protection throughout the product life cycle. In response to increasing materials costs in the corrugated industry, companies are focusing upon developing more efficient packaging designs. The scope of this project focuses on presenting alternative corrugated packaging designs for the fresh produce industry. Included are one piece designs, three piece bliss designs and alternative material exploration. This project presents the performance of new solutions by exploring their compressive strength before and after exposure to humidity.

Effects Of Thermo-Mechanical Loading From In-Situ Studies Of Eb-Pvd Thermal Barrier Coatings, Melan N. Jansz

Electronic Theses and Dissertations

The thermo-mechanical effects on the strain evolution within an EB-PVD thermal barrier coating (TBC) is presented in this work using in-situ characterization. Synchrotron X-ray diffraction at sector 1-ID at the Argonne National Laboratory provided both qualitative and quantitative in-situ data on the strain evolution under a thermal cycle with mechanical loading. The results show that at a critical combination of temperature and load, the stress in the thermally grown oxide (TGO) layer in the TBC reaches a tensile region. These significant findings enhance existing literature showing purely compressive strains within the TGO where mechanical loads have been neglected. The results …

Technique To Measure Heats Of Reaction Of Ti-B, Al-Ti-B, And Al-Ti-B4c Powder Blends, Andrew H. Baker

Dissertations, Master's Theses and Master's Reports - Open

In this research, a modification to initiation aid ignition in bomb calorimetry that involves systemically blending levels of boron and potassium nitrate initiation aids with a bulk structural energetic elemental power blend is developed. A regression is used to estimate the nominal heat of reaction for the primary reaction. The technique is first applied to the synthesis of TiB2 as a validation study to see if close proximity to literature values can be achieved. The technique is then applied to two systems of interest, Al-Ti-B, and Al-Ti-B4C. In all three investigations, x-ray diffraction is used to characterize the product phases …

Processing And Mechanical Properties Of Cast Aluminum Containing Scandium, Zirconium, And Ytterbium , Nicholas D. Johnson

Dissertations, Master's Theses and Master's Reports - Open

A series of aluminum alloys containing additions of scandium, zirconium, and ytterbium were cast to evaluate the effect of partial ytterbium substitution for scandium on tensile behavior. Due to the high price of scandium, a crucible-melt interaction study was performed to ensure no scandium was lost in graphite, alumina, magnesia, or zirconia crucibles after holding a liquid Al-Sc master alloy for 8 hours at 900 °C in an argon atmosphere. The alloys were subjected to an isochronal aging treatment and tested for conductivity and Vickers microhardness after each increment. For scandium-containing alloys, peak hardnesses of 520-790 MPa, and peak tensile …

Effects Of Silicon Content And Cooling Rate On Mechanical Properties Of Heavy Section Ductile Cast Iron , Meghan Haycock

Dissertations, Master's Theses and Master's Reports - Open

The effects of Si and cooling rate are investigated for their effect on the mechanical properties and microstructure. Three alloys were chosen with varying C and Si contents and an attempt to keep the remainder of the elements present constant. Within each heat, three test blocks were poured. Two blocks had chills – one with a fluid flowing through it to cool it (active chill) and one without the fluid (passive) – and the third block did not have a chill. Cooling curves were gathered and analyzed. The mechanical properties of the castings were correlated to the microstructure, cooling rate …

High Temperature, Low Cycle Fatigue Of A Hybrid Particulate/Fiber Aluminum Metal-Matrix Composite , Justin Clark

Dissertations, Master's Theses and Master's Reports - Open

The effect of shot particles on the high temperature, low cycle fatigue of a hybrid fiber/particulate metal-matrix composite (MMC) was studied. Two hybrid composites with the general composition A356/35%SiC particle/5%Fiber (one without shot) were tested. It was found that shot particles acting as stress concentrators had little effect on the fatigue performance. It appears that fibers with a high silica content were more likely to debond from the matrix. Final failure of the composite was found to occur preferentially in the matrix. SiC particles fracture progressively during fatigue testing, leading to higher stress in the matrix, and final failure by …

Structure And Properties Of Graphene Nano Disks (Gnd) With And Without Edge-Dopants, Pubodee Ratana-Arsanarom

Dissertations, Master's Theses and Master's Reports - Open

Graphene is one of the most important materials. In this research, the structures and properties of graphene nano disks (GND) with a concentric shape were investigated by Density Functional Theory (DFT) calculations, in which the most effective DFT methods - B3lyp and Pw91pw91 were employed.

It was found that there are two types of edges - Zigzag and Armchair in concentric graphene nano disks (GND). The bond length between armchair-edge carbons is much shorter than that between zigzag-edge carbons. For C24 GND that consists of 24 carbon atoms, only armchair edge with 12 atoms is formed. For a GND larger …

Effect Of Process Parameter On Temperature Distribution, Microstructure, And Mechanical Properties Of Self-Reacting Friction Stir Welded Aluminum Alloy 6061-T651, Monica Adriana Torres

Open Access Theses & Dissertations

Self-reacting friction stir welding is the latest FSW tool configuration developed, it employs two shoulders--one on top and one on the bottom of the workpiece-- this tool configuration offers many advantages over conventional welding techniques. However, the current lack of information and specifications limits its understanding and application. This investigation analyzed the effect of process parameters on temperature distribution, microstructure evolution, and final mechanical properties of 6061-T651 SR-FS welds. A factorial experiment was carried out, in which three-process parameters were analyzed--rotational speed, travel speed, and tool plunge force-- three levels were analyzed for each parameter, except for a tool plunge …

Calibration Of Alumina-Epoxy Nanocomposites Using Piezospectroscopy For The Development Of Stress-Sensing Adhesives, Amanda L. Stevenson

Electronic Theses and Dissertations

A non-invasive method to quantify the stress distribution in polymer-based materials is presented through the piezospectroscopic calibration of alumina-epoxy nanocomposites. Three different alumina volume fraction nanocomposites were created and loaded under uniaxial compression in order to determine the relationship between applied stress and the frequency shift of the R-lines produced by alumina under excitation. Quantitative values for six piezospectroscopic coefficients were obtained which represent the stress-sensing property of the nanocomposites. The results were applied to an alumina-filled adhesive in a single lap shear configuration demonstrating the capability of the technique to monitor R-line peak positions with high spatial resolution and …

Ballistic Projectile Metallurgical Issues And Fundamentals: Aerosol Production In Rod Penetration Erosion And Erosion Phenomena Associated With Railgun Development, Brenda Ivette Machado

Open Access Theses & Dissertations

The issue is derived from ballistic erosion as it relates to nanoparticle production and respiration of these particles as a health concern ballistic erosion and ballistic erosion as it relates to railgun performance. A common thread between these two issues is dynamic recrystallization (DRX). DRX has been demonstrated to be the dominant mechanism for solid-state flow associated with ballistic projectile/target penetration and interaction, friction-stir welding phenomena, and other high-strain rate deformation phenomena.

Aerosol particulates collected on filters from ballistic penetration and erosion events for W-Ni-Co and W-Ni-Fe kinetic energy rod projectiles penetrating steel target plates were observed to be highly …

Solving The Partial Differential Equation Of Vibrations With Interval Parameters Using The Interval Finite Difference Method, Brenda G. Medina

Open Access Theses & Dissertations

Accuracy and efficiency are among the main factors that drive today's innovative disciplines. As technology rapidly advances, efficiency takes on new meanings but what about accuracy? How accurate is accurate? Human error, uncertainties in measurement, and rounding errors are just some causes of inaccuracy. Interval Computations is an area that allows for such issues to be taken into account; for each measurement attained (for example), an interval can be built by considering the error associated with the measurement, and such an interval can be utilized in the mathematical computations of interest.

We consider the partial differential equation (PDE) of vibrations …

Development And Characterization Of The Oxidation Behavior Of Various High Temperature Niobium Based Alloys, Benedict Isabel Portillo

Open Access Theses & Dissertations

The oxidation response of various niobium based refractory alloys from the Nb-Mo-Si-B-X alloy system has been examined at temperatures between 700 and 1400°C in air. The development of these alloys was part of an ongoing effort to develop and discover a new materials system capable of replacing nickel based super alloys. Additions of titanium were found to provide limited oxidation resistance. A discontinuous layer of TiO2 was observed to from at temperatures above 1100°C. Alloys containing titanium additions were observed to suffer from pest oxidation at low and intermediate temperatures due to the development of Nb2O5. Poor oxidation resistance at …

The Effect Of Cr, Si And B On The Oxidation Behavior On Three Nb-Based Alloys, David Alvarez

Open Access Theses & Dissertations

Nb-based alloys are of particular interest to replace the current Ni-based superalloys for high-temperature structural applications. One important limitation to improve the efficiency of gas-turbine engines is the temperature limit of current materials being used. By allowing the temperature to increase, the efficiency will increase. Nb-based alloys have high melting points and adequate mechanical properties but the oxidation resistance is still inadequate.

This research focuses on the oxidation behavior of three Nb-based alloys to study the effect of Cr and Si variation and look at the effect of Boron. Boron can form a glassy borosilicate which is viscous at high …

Fabrication And Characterization Of Nanocrystalline Yttrium Oxide Thin Films For Electronic Device Applications, Mudavakkat Vikas Haridas

Open Access Theses & Dissertations

This thesis presents the optimization of growth conditions for fabricating nanocrystalline Yttrium Oxide (Y2O3) thin films on silicon and optical grade, high quality quartz substrates in order to study its structural, optical and electrical properties for electronic device applications.

Commercially Y2O3 has proven to be difficult to fabricate at high quality due to its high temperature growth requirements and the need to alter established fabrication methods for electronic devices. A high temperature requirement for high quality poses a problem for research and analysis. This calls upon for an optimization of the growth conditions to facilitate fabrication of thin films for …

Fundamental Studies Of Co-Base Superalloy Biomedical Prototypes Fabricated By Electron Beam Melting: Microstructures And Microstructural Architecture, Sara M. Gaytan

Open Access Theses & Dissertations

Rapid prototyping, especially electron beam melting (EBM) technology by ARCAM have proven to provide outstanding microstructural and mechanical properties on different alloys fabricated by this technology. Being a computer designed driven technology, complex components, that are hard or even impossible to fabricate by traditional manufacturing techniques, can be fabricated by layer-by-layer EBM technology.

Microstructural and mechanical properties are compared for an EBM femoral knee component prototype with a traditionally-fabricated and body-removed femoral knee implant. Block and cylindrical shape components fabricated by EBM were also analyzed for this project. The alloy utilized for these components is Co-26Cr-6Mo-0.2C characterized by the standards …

Preparation And Characterization Of Iron Oxide And Hydroxide Based Nanomaterials, Guillermo Carbajal Franco

Open Access Theses & Dissertations

Iron (Fe) oxides and hydroxides are common and abundant materials. They exhibit diverse crystal structures, properties and phenomena by virtue of which they find a wide range of scientific and technological applications. Controlled growth and manipulation of the specific structure and electronic behavior to meet the requirements of a given application is a challenging problem in view of many possible phases and composition of the resulting materials. The preparation method and experimental conditions will, therefore, significantly affect the properties and performance of Fe oxides and hydroxides. The goal of the project is to obtain Fe-based oxide/hydroxide catalytic materials and to …